GAUCHE DEFECTS, POSITIONAL DISORDER, DISLOCATIONS, AND SLIP PLANES INCRYSTALS OF LONG METHYLENE SEQUENCES

Conformational disorder in crystals of long methylene sequences in the form of gauche defects has been studied in the last few years in our laboratory by using large-scale molecular dynamics stimulations. The d istribution of gauche defects within crystals simulated under differen t conditions and temperatures has been extracted and is shown to depen d mainly on temperature and to some degree on external constraints. Th e crystal surfaces, and especially those that contain chain ends, have a higher probability for conformational disorder. The results supplem ent available experimental data and provide atomistic details about th is dynamic disorder. Plastic deformation could be produced by letting a compressed crystal expand in one direction. Positional disorder, dis locations, and slip planes were produced in this process and are detai led.